35 



GENERAL BIOLOGY 



fc 



This destruction of larval tissues during the pupal stage is 

 one of the most remarkable deviations from the ordinary 

 progressive course of the life cycle. Similar processes occur 

 wherever larval organs are to be made over. The tadpole's 

 tail does not drop off; that would be a waste of valuable 



organic materials. It is 

 reabsorbed: i. e., it is dis- 

 solved and transported 

 and used again for the 

 building of other parts. 

 The agents of the reabsorp- 

 tion in the tadpole are 

 leucocytes that have 

 turned temporarily to a 

 diet of muscle fibres (and 

 are called during their tis- 

 sue-eating period, phago- 

 cytes: the phenomenon is called phagocytosis see fig. 202). 



FIG. 202. Phagocytosis in the fat of the 

 abdomen of the iris weevil. /, fat ; 

 p, phagocytes. 



Some of the tissues of the insect larvae are eaten and 

 transported by phagocytes. Others appear to be self dis- 

 integrating; their nuclei divide extensively and become 

 very small and then gather about themselves the reinte- 

 grated remains of the old cytoplasm and of dissolved fat 

 cells, and fashion them into new cell bodies, often constitut- 

 ing organs of very different form in the adult. The process 

 is somewhat like a return to an embryonic condition, 

 followed by a new embryonic development, wherein the 

 fat of the larva stands in the stead of the yolk in the egg. 

 If at the height of metamorphosis one cut open a pupa 

 that has developed from any of the more degenerate larvas, 

 he finds little semblance of organs, the greater part of the 

 body being reduced to a fluid mass which flows out at every 

 cut. 



